In recent years, dementia, memory retention defect, aphasia, apraxia, psychosis, and Alzheimer's disease, increased by the large expansion of the elderly population, changes in the social environment, etc., have been an increasing social problem. In particular, the cause and therapy of Alzheimer's disease are still being investigated.
Although 1,2,3,4-tetrahydro-9-aminoacridine, abbreviated as THA, has recently been developed as a treating agent for Alzheimer's disease in the United States and has attracted attention, it has not yet obtained approval from the FDA (Food and Drug Administration). The reason for the disapproval appears to relate to the question of efficacy and adverse reactions of THA. Therefore, it has been keenly demanded to develop an antidementic agent having potent pharmacological effects and excellent safety. The development of THA has accelerated development of antidementics world-wide, but no drug having potent antidementic effect and excellent safety which relieves patients from dementia on the clinical stage has been developed.